diff --git a/collection.c b/collection.c
new file mode 100644
index 0000000..3919902
--- /dev/null
+++ b/collection.c
@@ -0,0 +1,77 @@
+#include "collection.h"
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+
+void array_push(
+    void** data, size_t* capacity, size_t* size, void* elem, size_t elem_size)
+{
+    if (!*capacity) {
+        *capacity = 4;
+    }
+    if (!*data) {
+        *data = malloc(elem_size * *capacity);
+        *size = 0;
+    }
+    if (*size >= *capacity) {
+        *capacity *= 2;
+        *data = realloc(*data, *capacity * elem_size);
+    }
+    memcpy((unsigned char*)*data + *size, elem, elem_size);
+    *size += 1;
+}
+
+static void push_kwpair(Hashmap* m, KwPair* pair)
+{
+    array_push((void**)&m->entries,
+        &m->entries_capacity,
+        &m->entries_size,
+        pair,
+        sizeof(*pair));
+}
+
+void hashmap_init(Hashmap* m)
+{
+    *m = (Hashmap) {
+        .entries = nullptr,
+        .entries_capacity = 8,
+        .entries_size = 0,
+    };
+}
+
+void hashmap_deinit(Hashmap* m)
+{
+    if (m->entries) {
+        for (size_t i = 0; i < m->entries_size; ++i) {
+            free(m->entries[i].key);
+        }
+        free(m->entries);
+    }
+}
+
+static KwPair* find_entry(Hashmap* m, const char* key)
+{
+    for (size_t i = 0; i < m->entries_size; ++i) {
+        if (strcmp(m->entries[i].key, key) == 0) {
+            return &m->entries[i];
+        }
+    }
+    return nullptr;
+}
+
+void hashmap_set(Hashmap* m, const char* key, void* val)
+{
+    KwPair* existing = find_entry(m, key);
+    if (existing) {
+        existing->val = val;
+        return;
+    }
+
+    push_kwpair(m, &(KwPair) { strdup(key), val });
+}
+
+void* hashmap_get(Hashmap* m, const char* key)
+{
+    KwPair* existing = find_entry(m, key);
+    return existing ? existing->val : nullptr;
+}
diff --git a/collection.h b/collection.h
new file mode 100644
index 0000000..bf92c0a
--- /dev/null
+++ b/collection.h
@@ -0,0 +1,26 @@
+#ifndef COLLECTION_H
+#define COLLECTION_H
+
+#include <stddef.h>
+
+void array_push(
+    void** data, size_t* capacity, size_t* size, void* elem, size_t elem_size);
+
+typedef struct {
+    char* key;
+    void* val;
+} KwPair;
+
+typedef struct {
+    KwPair* entries;
+    size_t entries_capacity;
+    size_t entries_size;
+} Hashmap;
+
+void hashmap_init(Hashmap* m);
+void hashmap_deinit(Hashmap* m);
+
+void hashmap_set(Hashmap* m, const char* key, void* val);
+void* hashmap_get(Hashmap* m, const char* key);
+
+#endif
diff --git a/examples/hello.c b/examples/hello.c
index 7583bb3..64d917b 100644
--- a/examples/hello.c
+++ b/examples/hello.c
@@ -1,6 +1,6 @@
-#include <stdio.h>
+int puts(const char* __s);
 
 int main()
 {
-    printf("hello\n");
+    puts("hello");
 }
diff --git a/parse.c b/lex.c
similarity index 56%
rename from parse.c
rename to lex.c
index 6119f43..35b5608 100644
--- a/parse.c
+++ b/lex.c
@@ -4,11 +4,6 @@
 #include <stdio.h>
 #include <string.h>
 
-// phases:
-// https://en.cppreference.com/c/language/translation_phases
-
-// phase 1 - source chars
-
 void source_char_iter_init(SourceCharIter* r, const char* text)
 {
     *r = (SourceCharIter) {
@@ -19,7 +14,7 @@ void source_char_iter_init(SourceCharIter* r, const char* text)
     };
 }
 
-SourceChar source_iter_next(SourceCharIter* r)
+Char source_iter_next(SourceCharIter* r)
 {
     char ch = r->text[r->i];
     int line = r->line;
@@ -35,14 +30,12 @@ SourceChar source_iter_next(SourceCharIter* r)
         r->i += 1;
     }
 
-    return (SourceChar) { ch, line, col };
+    return (Char) { ch, line, col };
 }
 
-// phase 2 - logical source lines
-
 void lsl_iter_init(LslCharIter* r, SourceCharIter* source_char_iter)
 {
-    SourceChar curr = source_iter_next(source_char_iter);
+    Char curr = source_iter_next(source_char_iter);
 
     *r = (LslCharIter) {
         .source_char_iter = source_char_iter,
@@ -50,30 +43,30 @@ void lsl_iter_init(LslCharIter* r, SourceCharIter* source_char_iter)
     };
 }
 
-LslChar lsl_iter_next(LslCharIter* r)
+Char lsl_iter_next(LslCharIter* r)
 {
-    SourceChar next = source_iter_next(r->source_char_iter);
+    Char next = source_iter_next(r->source_char_iter);
 
     if (r->curr.ch == '\\' && next.ch == '\n') {
         r->curr = source_iter_next(r->source_char_iter);
         return lsl_iter_next(r);
     }
 
-    LslChar lsl_char = { r->curr.ch, r->curr.line, r->curr.col };
+    Char lsl_char = { r->curr.ch, r->curr.line, r->curr.col };
 
     r->curr = next;
     return lsl_char;
 }
 
-// phase 3 - preprocessor tokens
-
 void lexer_init(Lexer* r, LslCharIter* lsl_char_iter)
 {
-    LslChar curr = lsl_iter_next(lsl_char_iter);
+    Char curr = lsl_iter_next(lsl_char_iter);
 
     *r = (Lexer) {
         .lsl_char_iter = lsl_char_iter,
         .curr = curr,
+        .lex_whitespace = false,
+        .lex_headername = false,
     };
 }
 
@@ -82,14 +75,14 @@ static Tok tok(TokTy ty, const char* text, int line, int col)
     return (Tok) { ty, strdup(text), line, col };
 }
 
-static bool l_done(Lexer* l)
+static bool done(Lexer* l)
 {
     return l->curr.ch == '\0';
 }
 
 constexpr size_t max_token_text_len = 64;
 
-static void l_step(Lexer* l, char text[], size_t* text_len)
+static void step(Lexer* l, char text[], size_t* text_len)
 {
     assert(*text_len < max_token_text_len);
     text[*text_len] = l->curr.ch;
@@ -106,16 +99,19 @@ Tok lexer_next(Lexer* l)
     char text[max_token_text_len] = "";
     size_t text_len = 0;
 
-    if (l_done(l)) {
+    if (done(l)) {
         return tok(Tok_Eof, text, line, col);
     }
 
     bool matched = false;
     while (strchr(" \t\r", l->curr.ch)) {
         matched = true;
-        l_step(l, text, &text_len);
+        step(l, text, &text_len);
     }
     if (matched) {
+        if (l->lex_whitespace) {
+            return tok(Tok_Whitespace, text, line, col);
+        }
         return lexer_next(l);
     }
 
@@ -124,7 +120,7 @@ Tok lexer_next(Lexer* l)
         || (matched && l->curr.ch >= '0' && l->curr.ch <= '9')
         || strchr("_", l->curr.ch)) {
         matched = true;
-        l_step(l, text, &text_len);
+        step(l, text, &text_len);
     }
     if (matched) {
         return tok(Tok_Ident, text, line, col);
@@ -133,52 +129,75 @@ Tok lexer_next(Lexer* l)
     while ((l->curr.ch >= '1' && l->curr.ch <= '9')
         || (matched && l->curr.ch == '0')) {
         matched = true;
-        l_step(l, text, &text_len);
+        step(l, text, &text_len);
     }
     if (matched) {
         return tok(Tok_Int, text, line, col);
     }
 
-    if (l->curr.ch == '"') {
-        l_step(l, text, &text_len);
-        while (l->curr.ch != '"') {
-            if (l->curr.ch == '\\') {
-                l_step(l, text, &text_len);
-                if (l_done(l))
-                    break;
-            }
-            l_step(l, text, &text_len);
+    if (l->lex_headername && (l->curr.ch == '"' || l->curr.ch == '<')) {
+        char ter = l->curr.ch == '<' ? '>' : '"';
+        while (l->curr.ch != '\0' && l->curr.ch != '\n' && l->curr.ch != ter) {
+            step(l, text, &text_len);
         }
-        if (l_done(l) || l->curr.ch != '"') {
-            fprintf(stderr, "error: malformed string literal\n");
+        if (l->curr.ch != ter) {
+            fprintf(stderr,
+                "error: malformed header name, expected '%c' on line %d\n",
+                ter,
+                l->curr.line);
             return lexer_next(l);
         }
-        l_step(l, text, &text_len);
+        step(l, text, &text_len);
+        return tok(Tok_HeaderName, text, line, col);
+    }
+
+    if (l->curr.ch == '"') {
+        step(l, text, &text_len);
+        while (l->curr.ch != '"') {
+            if (l->curr.ch == '\\') {
+                step(l, text, &text_len);
+                if (done(l))
+                    break;
+            }
+            step(l, text, &text_len);
+        }
+        if (done(l) || l->curr.ch != '"') {
+            fprintf(stderr,
+                "error: malformed string literal on line %d\n",
+                l->curr.line);
+            return lexer_next(l);
+        }
+        step(l, text, &text_len);
         return tok(Tok_Str, text, line, col);
     }
 
     if (l->curr.ch == '\'') {
-        l_step(l, text, &text_len);
+        step(l, text, &text_len);
         if (l->curr.ch == '\\') {
-            l_step(l, text, &text_len);
+            step(l, text, &text_len);
         }
-        if (!l_done(l)) {
-            l_step(l, text, &text_len);
+        if (!done(l)) {
+            step(l, text, &text_len);
         }
-        if (l_done(l) && l->curr.ch != '\'') {
-            fprintf(stderr, "error: malformed character literal\n");
+        if (done(l) && l->curr.ch != '\'') {
+            fprintf(stderr,
+                "error: malformed character literal on line %d\n",
+                l->curr.line);
             return lexer_next(l);
         }
-        l_step(l, text, &text_len);
+        step(l, text, &text_len);
         return tok(Tok_Char, text, line, col);
     }
 
-    if (strchr("\n;(){}", l->curr.ch)) {
+    if (strchr("\n;(){}#", l->curr.ch)) {
         TokTy ty = (TokTy)l->curr.ch;
-        l_step(l, text, &text_len);
+        step(l, text, &text_len);
         return tok(ty, text, line, col);
     }
-    fprintf(stderr, "error: illegal character '%c'\n", l->curr.ch);
-    l_step(l, text, &text_len);
+    fprintf(stderr,
+        "error: illegal character '%c' on line %d\n",
+        l->curr.ch,
+        l->curr.line);
+    step(l, text, &text_len);
     return lexer_next(l);
 }
diff --git a/parse.h b/parse.h
index b77b871..1daadac 100644
--- a/parse.h
+++ b/parse.h
@@ -1,13 +1,19 @@
 #ifndef PARSE_H
 #define PARSE_H
 
+#include "collection.h"
 #include <stddef.h>
 
+// phases:
+// https://en.cppreference.com/c/language/translation_phases
+
+// phase 1 - source chars
+
 typedef struct {
     char ch;
     int line;
     int col;
-} SourceChar;
+} Char;
 
 typedef struct {
     const char* text;
@@ -17,36 +23,35 @@ typedef struct {
 } SourceCharIter;
 
 void source_char_iter_init(SourceCharIter* r, const char* text);
-SourceChar source_iter_next(SourceCharIter* r);
+Char source_iter_next(SourceCharIter* r);
 
-typedef struct {
-    char ch;
-    int line;
-    int col;
-} LslChar;
+// phase 2 - logical source lines
 
 typedef struct {
     SourceCharIter* source_char_iter;
-    SourceChar curr;
+    Char curr;
 } LslCharIter;
 
 void lsl_iter_init(LslCharIter* r, SourceCharIter* source_char_iter);
-LslChar lsl_iter_next(LslCharIter* r);
+Char lsl_iter_next(LslCharIter* r);
+
+// phase 3 - preprocessor tokens
 
 typedef enum {
     Tok_Eof,
-    Tok_Eol,
     Tok_Ident,
     Tok_Int,
     Tok_Str,
     Tok_Char,
+    Tok_Whitespace,
     Tok_HeaderName,
-    Tok_Newline = '\n', // NOTE: has value 10
+    Tok_Eol = '\n', // NOTE: has value 10
     Tok_Semicolon = ';',
     Tok_LParen = '(',
     Tok_RParen = ')',
     Tok_LBrace = '{',
     Tok_RBrace = '}',
+    Tok_Hashtag = '#',
 } TokTy;
 
 typedef struct {
@@ -58,10 +63,30 @@ typedef struct {
 
 typedef struct {
     LslCharIter* lsl_char_iter;
-    LslChar curr;
+    Char curr;
+    bool lex_whitespace;
+    bool lex_headername;
 } Lexer;
 
 void lexer_init(Lexer* r, LslCharIter* lsl_char_iter);
 Tok lexer_next(Lexer* l);
 
+// phase 4 - preprocessor
+
+typedef struct DefToks DefToks;
+
+typedef struct {
+    Lexer* lexer;
+    Tok curr;
+
+    DefToks* deftoks;
+    size_t deftoks_cap;
+    size_t deftoks_size;
+    Hashmap defs;
+} Preproc;
+
+void preproc_init(Preproc* p, Lexer* lexer);
+void preproc_deinit(Preproc* p);
+Tok preproc_next(Preproc* p);
+
 #endif
diff --git a/preproc.c b/preproc.c
new file mode 100644
index 0000000..40aac23
--- /dev/null
+++ b/preproc.c
@@ -0,0 +1,158 @@
+#include "collection.h"
+#include "parse.h"
+#include <assert.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct DefToks {
+    Tok* toks;
+    size_t toks_cap;
+    size_t toks_size;
+};
+
+void preproc_init(Preproc* p, Lexer* lexer)
+{
+    Tok curr = lexer_next(p->lexer);
+
+    *p = (Preproc) {
+        .lexer = lexer,
+        .curr = curr,
+        .deftoks = nullptr,
+        .deftoks_cap = 0,
+        .deftoks_size = 0,
+        .defs = { },
+    };
+
+    hashmap_init(&p->defs);
+}
+
+void preproc_deinit(Preproc* p)
+{
+    if (p->deftoks) {
+        free(p->deftoks);
+    }
+    hashmap_deinit(&p->defs);
+}
+
+static void step(Preproc* p)
+{
+    p->curr = lexer_next(p->lexer);
+}
+
+Tok preproc_next(Preproc* p)
+{
+    if (p->curr.ty == '#') {
+        step(p);
+        Tok kw = p->curr;
+
+        if (strcmp(kw.text, "define") == 0) {
+            step(p);
+            if (p->curr.ty != Tok_Ident) {
+                fprintf(stderr,
+                    "error: expected identifier on line %d\n",
+                    p->curr.line);
+                exit(1);
+            }
+            Tok ident_tok = p->curr;
+
+            p->lexer->lex_whitespace = true;
+            step(p);
+            p->lexer->lex_whitespace = false;
+
+            if (p->curr.ty == '(') {
+                // function-like macro
+                assert(false && "not implemented");
+            }
+
+            DefToks toks = { };
+
+            while (p->curr.ty != Tok_Eof && p->curr.ty != Tok_Eol) {
+                array_push((void**)&toks.toks,
+                    &toks.toks_cap,
+                    &toks.toks_size,
+                    &p->curr,
+                    sizeof(p->curr));
+                step(p);
+            }
+
+            array_push((void**)&p->deftoks,
+                &p->deftoks_cap,
+                &p->deftoks_size,
+                &toks,
+                sizeof(toks));
+
+            DefToks* deftoks = &p->deftoks[p->deftoks_size - 1];
+            hashmap_set(&p->defs, ident_tok.text, deftoks);
+
+            return p->curr;
+        } else if (strcmp(kw.text, "undef") == 0) {
+            step(p);
+
+            if (p->curr.ty != Tok_Ident) {
+                fprintf(stderr,
+                    "error: expected identifier on line %d\n",
+                    p->curr.line);
+                exit(1);
+            }
+            Tok ident_tok = p->curr;
+
+            if (p->curr.ty != Tok_Eof && p->curr.ty != Tok_Eol) {
+                fprintf(stderr,
+                    "error: unexpected extra tokens on line %d\n",
+                    p->curr.line);
+                exit(1);
+            }
+
+            hashmap_set(&p->defs, ident_tok.text, nullptr);
+
+            return p->curr;
+        } else if (strcmp(kw.text, "include") == 0) {
+            p->lexer->lex_headername = true;
+            step(p);
+            p->lexer->lex_headername = false;
+
+            if (p->curr.ty != Tok_HeaderName) {
+                fprintf(stderr,
+                    "error: expected header name line %d\n",
+                    p->curr.line);
+                exit(1);
+            }
+
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "if") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "ifdef") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "ifndef") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "else") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "elif") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "elifdef") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "elifndef") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "endif") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "line") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "embed") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "error") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "warning") == 0) {
+            assert(false && "not implemented");
+        } else if (strcmp(kw.text, "pragma") == 0) {
+            fprintf(stderr,
+                "error: '%s' is not a preprocessor instruction on line %d\n",
+                kw.text,
+                kw.line);
+            exit(1);
+        }
+    }
+
+    return p->curr;
+}